1. Field of the Invention
The invention relates to a method according to the preamble of claim 1. The invention especially relates to a method of cleaning processing equipment, in particular filters, such as membrane filters, which are used for producing liquid foodstuffs such as milk (or milk products), fruit juices, beer, soft drinks (such as lemonades), cider, wine, sherry, port, distilled drinks and the like.
2. Description of Related Art
In the food industry and sewage purification plants, use is being made to an increasing extent of membrane filters, in particular polymeric membranes such as, polysulphone, polyethersulphone (with or without polyvinylpyrrolidone) and certain types of polyamides, and ceramic membranes for removing insoluble matter from beverages and other liquids. Such membranes ensure an expedient removal of undesirable constituents, in particular micro-organisms such as algae, fungi, yeast, and bacteria (exudates).
However, the permeability of such membrane filters, also expressed as flux, decreases in the course of time and the membranes may become blocked even after a relatively short time, i.e. sometimes even within less than one hour, because components from the material to be treated are adsorbed or absorbed or precipitated on surfaces of the apparatus, which is undesirable. The consequence is that the process has to be stopped in order to clean the membranes. The blocked filters can be restored, for example by rinsing them through in the opposite direction, a process known as back-flushing. This can be seen as a mechanical solution. However, that is a complicated process and is only a temporary and not satisfactory solution, since after each step the initial flux (at the same trans membrane pressure) is lower than before and on long term the contamination accumulates to such an extent that the filter is completely blocked. Moreover, it is difficult to remove some persistent organic contaminants in this way.